Synthesis of iminodiacetonitrile



Patented June 13, 1950 A SYNTHESIS or IMINotimeE'roNr'rmm;

Henry T. Thompson, Easton, Pa., assignor to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware 'No Dr-awin'g."Application August 8,1946,

Serial No. 689,207

3 Claims. (01. 260-4655) I,

This invention relates to the synthesis of nitriles and particularly anew method for preparing 'iminodiacetonitrile, I-lN(CI-IzCN)2.

Iminodiacetonitrile has beenprepared heretofore by reaction betweenhexamethylenetetramine and hydrogen cyanide, but the process has beenunsatisfactory and wasteful because of the poor yield ofimododiacetonitrile obtained, and because the reaction is'so slow thatit requires several days for completion.

It has also been disclosed'heretofore '[Polstorfi and Meyer, Ber. 45,1905-12 (1912)] that in the synthesis of nitrilotriacetic acid byreaction between potassium cyanide and aqueous formaldeare produced.Polsdorfl? and Meyer have attempted to explain the formation ofpotassium iminodiacetate by postulating that underthe alkalineconditions prevailing a reaction may take place betweenamino-acetonitrile and formaldehyde cyanhydrin to formiminodiacetonitrile which may then react with the alkali to form thesalt of iminodiac'etic acid. The said postulated'process, however, hasnot been useful for the synthesis'of iminodiacetonitrile.

An object of this invention is to provide a process wherebyiminodiacetonitrile may be prepared without appreciable loss of nitrile.Another object is to provide a-process for the manufacture ofiminodiacetonitrile which produces the said nitrile substantially freefrom contamination by other materials such as nitrilotriacetoriitrile.

These and other objects are accomplished in accordance with thisinvention by reacting aminoacetonitrile with formaldehyde cyanhydrin ata temperature of about 50 .C. to 150 0., in the absence of alkali (i.e., alkaline materials such as hydroxides, carbonates, cyanides, etc. ofthe alkali metals, alkaline earth metals and the like), the initialmolal radio of aminoacetonitrile to formaldehyde cyanhydrin being about"1:03. to 111.5. In contrast with the postulated process of Polsdorff andMeyer, it has been discovered in accordance with this invention that, atslightly elevated temperatures, aminoacetonitrile and formaldehydecyanhydrin, in the presence of alkali, are rapidly (and sometimesviolently) decomposed, so that it is essential in the practice of thisinvention to eliminate any traces of alkaline catalysts. One method foraccomplishing this result is to add to the reaction mixture about 0.001to 0.5% of a mineral acid stabilizer, based on the initial weight of theformaldehyde cyanhydrin. The presence of the said mineral acidstabilizer is not indispensably necessary in the hyde, minor amounts ofpotassium iminodiacetate practice of the invention, provided, of course,that care is taken to avoid the presence of even small traces of alkali.The invention, therefore, contemplates the synthesis ofiminodiacetonitrile by heating aminoa'cetonitrile with formaldehydecyanhydrinin the aforesaid molal proportions,

"but preferably in about equimolal quantities, in

the 'absence of alkaline catalysts. In a specific embodiment, thepresent invention contemplates the synthesis of iminodiacetonitrilebyheating substantially equimolal quantitles or aminoacetonitrile andformaldehyde cyanhydrin at a relatively high temperature within theaforesaid range, whereby a rapid reaction between aminoacetonitrile andformaldehyde cyanhydrin takes place without excessive decomposition ofthe reactants, thus producing imino'cliacetonitrile in very good yield.Therefore, in a preferred method of practicing the invention, the saidreactants are heated at a temperature of about C., i'n'the absence ofalkali, whereby a reaction producing iminodiacetonitrile takes place.Decomposition due to prolonged heating is prevented by stopping thereaction after a total reaction time not exceeding about 15 minutes,preferably by quickly cooling the mixture. Under the aforesaid preferredconditions, only a small quantity of tarry by-product resulting from thedecomposition of the constituents of the reaction mixture is produced;The temperature range within which this rapid reaction takes placewithout the formation of excessive quantities of decomposition productsis some what narrow, preferably about 135 C. to C.

The aminoacetonitrile used as one of the reactants-in accordance withthis invention may be prepared by heating formaldehyde cyanhydrinwith'anhydro'us ammonia, or by any other suitable process." While pureaminoacetonitrile may be used, it is'frequently convenient to employaminoacetonitrile'in the form-"of an aqueous solution'. Similarly; theformaldehyde cyanhydrin ants employed in the practice of the invention,the preferred stabilizers being mineral acids, particularly phosphoricacid.

In one manner of carrying out the invention, the formaldehyde cyanhydrinand aminoacetonitrile are mixed together and heated in a flask for therequired reaction time, and the resulting mixture is thereafter chilledwhereby the iminodiacetonitrile separates therefrom in the form ofcrystals.

The invention may be illustrated further by means of the followingexamples:

Example 1.A mixture containing; 17.1 grams of aminoacetonitrile and 5.3grams of formaldehyde cyanhydrin (containing a few dropsof phosphoricacid per liter) was heated onthe steam bath at a temperature of about100C. for one hour. The resulting mixture was cooled by means of an icebath whereby crystals of iminodiacetonitrile were deposited. The yieldof iminodiacetonitrile was about 70% -of the theoretical.

Example 2.-The mixture containing 58 grams (one mol) of formaldehydecyanhydrin and 57 grams: (one mol) of aminoacetonitrile was heatedtogether in a flask by means of an oil bath until the reaction mixturereached a temperature of 140 C. After about 5 minutes, a vigorous'reaction took place with evolution of hydrogen cyanide and water. Thereaction mixture was maintained at temperature of 140 C. for a totalreaction time of minutes. Upon cooling, the product crystallized forminga reddish brown solid. Four such runswere made, after which the crudeproducts were combined and iminodiacetonitrile was separated therefromby extraction with hot benzene until only a brown resinous materialremained. The iminodiacetonitrile crystallized from the benzene oncooling in long, colorless needles. These were removed by filtration anddried. The total weight of iminodiacetonitrile thus obtained was 296grams, which corresponds to a yield of about 78%.

It is evident that numerous changes may be made in the manner ofconducting the reaction between aminoacetonitrile and formaldehydecyanhydrin without departing from the scope of this invention. Forexample, the reaction'may be carried out in a closed pressure-resistingvessel, and at pressures higher'than atmospheric. The reaction heat maybe dissipated through cooling coils, water-jackets, or other convenientmeans. In embodiments in which an acidic stabilizer is employed, thestabilizer may be removed in the form of an insoluble salt prior toisolating the product, if desired. While in the examples the inventionis illustrated by means of batchwise operation, it is to be understoodthat excellent results also are obtained. in continuous operation. Inthe continuous, process, tubular converters, within which the reactantsare heated at controlled short reaction times,

" of about-0.001 to-0.5% of a mineral acid stabilizer based on theinitial weight of the formaldehyde cyanhydrin, the initial molal ratioof amino- -acetonitrile to formaldehyde cyanhydrin being about 1:0.3 to111.5, and thereafter separating iminodiacetonitrile from the resultingmixture. 2. The process set forth in claim 1, in which the said mineralacid stabilizer is phosphoric acid.

3. A process for the synthesis of iminodiacetonitrilewhich comprisesheating a reaction mixture consisting of aminoacetonitrile andformaldehyde cyanhydrin in equimolal proportions at a temperature ofabout to 0., whereby a reaction producing iminodiacetonitrile takesplace, maintaining the resulting reaction mixture at the said reactiontemperature for a total reaction time not exceeding about 15 minutes,and thereafter cooling the resulting mixture and separatingiminodiacetonitrile therefrom.

HENRY T. THOMPSON.

REFERENCES CITED The following references are of record in the fileofthis patent:

UNITED STATES PATENTS Number Name 7 Date 2,085,679 Gluud et al. June 29,1937 2,175,805 Jacobson Oct. 10, 1939 2,205,995 Ulrich et al June 25,1940 2,228,271 Jacobson et al Jan. 14, 1941 2,405,966 Loder Aug. 20,1946 2,407,645 Bersworth Sept. 17, 1946 FOREIGN PATENTS Number CountryDate 388,874 Great Britain Mar. 9, 1933 638,071 Germany Nov. 9, 1936673,590 Germany Mar. 28, 1939 OTHER REFERENCES .Stadnikoff, Ber. Deut.Chem., vol. 40, pp. 1014 1017 (1907).

Polstorff et al., Ber. Deut. Chem., vol. 45, pp. 1905-1912 (1912).

Dubsky, Ber. Deut. Chem., vol. 49, pp. 1048-9 (1916).

1. A PROCESS FOR THE SYNTHESIS OF IMINODIACETONITRILE WHICH COMPRISESHEATING AMINOACETONITRILE WITH FORMALDEHYDE CYANHYDRIN AT A TEMPERATUREOF ABOUT 100* TO 150*C., IN THE PRESENCE OF ABOUT 0.001 TO 0.5% OF AMINERAL ACID STABILIZER BASED ON THE INITIAL WEIGHT OF THE FORMALDEHYDECYANHYDRIN, THE INITIAL MOLAL RATIO OF AMINOACETONITRILE TO FORMALDEHYDECYANHYDRIN BEING ABOUT 1:0.3 TO 1:1.5, AND THEREAFTER SEPARATINGIMINODIACETONITRILE FROM THE RESULTING MIXTURE.